Exhaust gas recirculation EGR valves are generally applied in automotive internal combustion engine emission controls for metering exhaust gas for combination with a "clean" air charge into the engine. EGR valves typically include an orifice and a pintle on an end of shaft driven by an electromagnetic actuator acting against the force of a return spring. The EGR valve is positioned in the exhaust gas recirculation flow path so that all recirculated exhaust gas must pass through the valve orifice. In its normally closed position, the pintle is sealably engaged with the valve orifice to block exhaust gas flow through the orifice. The pintle must securely seal the orifice when closed to ensure that no exhaust gas flows through the orifice. Even a small flow of exhaust gas through the orifice can sufficiently dilute the engine fresh air charge to alter engine operation and potentially reduce engine performance stability and potentially increase engine emissions. The position of the EGR valve is precisely controlled so that exactly the correct dilution of the fresh air charge is maintained under all conditions. Too much or too little dilution can perceptibly disrupt engine stability and can increase engine emissions.
The recirculated engine exhaust gas, laden with contaminants, comes in contact with many moving parts within the EGR valve including the valve orifice, pintle and shaft. Contaminants may be deposited on such moving parts, and may accumulate over time. The contaminants may accumulate to a level affecting EGR valve performance. For example, buildup of contaminants on the shaft can reduce clearance between the shaft and the bore (or bearing) through which the shaft travels and can eventually contact the bore, increasing the frictional load on the shaft which reduces dynamic performance and can result in restriction in valve motion. Additionally, build-up on the pintle or about the orifice can prevent a sealed engagement between the pintle and the orifice. The contamination can increase a difference between actual and desired dilution of the engine fresh air charge, potentially increasing engine emissions and decreasing engine performance.
Concern about contaminant build-up on EGR valves has lead to such remedial measures as design and application of complex, expensive EGR valve apparatus, and intrusive EGR valve maintenance procedures. The maintenance procedures include periodic cycling of the EGR valve pintle and shaft along its range of motion during engine operation to scrape off the contaminant build-up or to knock contaminants loose. Such cycling may reduce contaminant build-up but includes an emissions and performance penalty by driving a dilution level away from a desired level simply to provide for EGR valve maintenance. Engine emissions may increase and the engine may perform perceptibly below operator expectation.
It would therefore be desirable to maintain the EGR valve in a condition supporting precision EGR control with an unintrusive valve maintenance method having no associated engine performance or emissions penalty.